As shown in FIG. 1, in order to attain the function of tool changing, the spindles of the prior art's machine center are all equipped with a tool pulling mechanism in their shafts. The said tool pulling mechanism consists of a tool 1, a spindle shaft 2, balls 3, a draw bar 4 and springs 5 etc. The tool pulling force of the said tool pulling mechanism is mainly generated by the springs contained in the mechanism and is approximately equal to the acting spring force. The magnitude of the said tool pulling force can be as high as 700.about.2000 kg or higher depending on the designed capacity of the said tool pulling mechanism.
But the prior art's tool pulling mechanism as stated above, must have the thrust, generated by the tool releasing hydraulic cylinder, greater than the tool pulling force to dominate the spring action, i.e. the tool releasing force must be greater than the tool pulling force such that it can make the tool separate from the shaft. Limiting by this, the force releasing hydraulic cylinder and the bearing loading as well as the shaft spring can not be reduced, which is inconvenient to the part selection.
Therefore, it is understood that the spindle tool pulling mechanism of the prior art as stated above is obviously inconvenient and having shortcomings in practical usage and on the manufacturing production and is expected to have rooms to improve.
Inasmuch, the inventors, having the thinking of improving the aforesaid shortcomings and being accompanied with the application of the theory, have devoted themselves in studies and eventually produced the present invention with rational design and effective improvement on the aforesaid shortcomings.